Monitoring the area behind motor vehicles is a highly topical subject. Reversing can present significant hazards, since the driver cannot see the whole of the hazardous area behind. There is therefore a risk of colliding with buildings, goods, persons or other objects. This is especially a problem when reversing commercial vehicles or construction machinery. For this reason, a range of methods for monitoring the area behind the vehicle have already been proposed. Conventional rear area monitoring systems mostly use distance sensors that are installed at one location or in one plane at the rear of the vehicle, and that indicate the distance from an obstacle. Use is made of the ultrasonic echo method, employing ultrasonic sensors, which in themselves are known, but which nevertheless only have a limited detection range, so that, generally, it is not possible to detect all the objects behind a vehicle.
Storing limit values in a vehicle, in particular for the width and height of the vehicle, is also known—see, e.g., DE 199 28 679 A1. The position of the vehicle is detected; as the vehicle approaches relevant structures, the vehicle data is compared against the data saved about the relevant structure. If the vehicle cannot pass the structure because it is too high or too wide, a warning is issued to the driver.
DE 10 2004 015 749 A1 discloses equipment for determining the possibility of a vehicle passing. The equipment estimates whether the height of the vehicle and/or the width of the vehicle permits it to pass between obstacles.
DE 10 2007 053 989 A1 discloses an arrangement for warning about obstacles affording insufficient height to pass and/or insufficient width to pass. Overhead obstacles and/or lateral obstacles in front of the vehicle are scanned in order to capture passage-related data from the obstacles, whereby the surface of the road is also scanned at the same time. The ascertained passage-related data from the obstacles is compared against passage-related data from the vehicle. A warning signal is issued to the driver if the passage-related data from the vehicle is greater than or equal to the passage-related data from the obstacles. The warning signals may be of a visual, audible or haptic nature.
Groeneveld sells an object detection system under the name GREENSIGHT. This includes an active camera detection system that provides the driver with a complete image of the situation behind the vehicle. In addition to the camera detection system, the Groeneveld object detection system employs a sensor system that uses ultrasound to scan the area behind the vehicle. The detection area is distributed over three zones. The closer the object, the more insistent visual and audible warning signals become. The object detection system can be used with two additional ultrasonic units at the top corners of the vehicle in order to detect objects such as hanging signs, half-open roller doors and tree branches. In this known system, however, only the outer edges of the vehicle are monitored.
The known rear area monitoring systems offer good coverage of the surface of the monitoring region. The monitoring region is not sufficiently covered at height, however.